Electrical circuits



June 5, 1928.

l W. AUSTIN ELBCTRI CAL CIRCUITS Filed Jan. 19, 1924 Elma rte;

Louis 14 Ava tin,

Patented June 5, 1928.

UNIITEDISTATES 1,672,018 PATENT. OFFICE.

LouIs w. Austria, or'wasnme'ron, nrs'rn'rcror ooLumBm ELECTRICAL CIRCUITS.

Applicationfiled January 19, 1924. SerialNo. 687,281.

My invention relates generally to electri cal circuits, and particularlyto those in which high frequency electrical currents are pro electrode vacuum tube oscillator having coupled grid and plate circuits to produce oscillations, the period of the oscillations being, set by the period of one or the other of these circuits, that variations in the filament temperature or variations inthe plate circuit energy supply potential will cause vari ations in the frequency of the oscillations, and these variations become particularly noticeable in receiving byheterodyne at the higher frequency where a slight change in the frequency of a locally generated oscillation produces a substantial changefin the frequency of the beat'oscillations, or may even cause the beat oscillations to vary beyond'the range of audibility.

It is the principal purpose of my invention to prevent variations within the vacuum tube from materially influencing the constants of the circuit. determining the period of the oscillations of the system.-

My invention will be best understood by reference to the accompanying drawing in which A represents a conventional type of antenna coupled to a secondary oscillatory circuit containing inductances L and L and capacityC the couplingv being had with the antenna inductance L circuit is connected to the grid G and filament F of the vacuum tube VT through a very small capacity C and may include a serially included resistance R R is a resistance of the order of megohms inshunt to the capacity C ordinarily termed a grid leak. The vacuum tube VT also has a plate circuit including inductance L4, telephones T and battery B Condenser (1 is the usual radio frequency by-pass around the high impedance telephones T. The grid and plate circuits are interlinked, through This oscillatory the coupling between the inductance L and inductance L Battery, B provides for heating the filament F, and rheostat R permits of varying the amount of filament current.

The connection of the filament terminalof the plate circuit to the battery B is shown as-variable, to permit of varying the plate potential.

It has been the practice heretofore to provide a condenser in the position of my, condenser C shunted by'a grid leak It in circuit arrangements such as I have illustrated and described, but the prior practice has never made this condenser of sufficiently low capacity to effectively prevent variations in the vacuum tube from materially affecting the period of the oscillatory circuit L L and C Ordinarily if the conditions in the tube vary so as to alter the impedance of the internal path between the grid G and the filament F, these variations acting in shunt with the condenser C cause variations in the period of the oscillations. By making the capacity of C sufliciently small so that the capacity reaction in this condenser is the controlling reaction in the circuit produced by the connections of the oscillatory circuit to the grid and filament of the vacuum tube,

the variations in the tube will not cause subi stantial variations in the period of the oscillatory circuit. vI have also found thatin some cases thejcontrol of the constancy of the generated frequency is improved by inserting a resistance R of' several hundred ohms. It is common practice to use a grid condenser inthe location shown by my condenser C of 250 mic'ro-microfarads and above, and I have found that by reducing this capacity to the order of 25 micro-microfarads I have been able to generate oscillations of the order of 1000 kilo-cycles, and I use these oscillations for the reception of sustained wave signals by the heterodyne method without any noticeable change in frequency under varied conditions in the vacuum tube. In fact I prefer toemploy a tight fixed coupling between induct'ances L and L and vary the strength of the oscillations by varying a vacuum tube detector a grid-filament circuit and a plate-filament circuitincluding a regenerative inductance, the comblnation 1n the grid-filament'clrcult of a secondary i inductance, a second inductance in series therewith and coupled to the regenerative inductance in the plate-filament circuit, a tunlng condenser 1n parallel With the secondary inductance and the second inductance forming an oscillatory circuit therewith, a grid-condenser and grad-leak 111 series W1th the osc llatory c1rcu1t 1n the gr d-filament circuit and a resistance in series With the 0s cillatory circuit and, the grid-condenser.

' LOUIS XV. AUSTIN. 

